1. Technical Field
The present invention relates to decoding devices, decoding methods, and receiving devices concerning compressed image, and more particularly to a decoding device, a decoding method, and a receiving device for each of which a high data processing capability is required.
2. Background Art
Conventionally, among technologies of performing video coding (hereinafter, referred to simply as “coding”) using a difference between pictures, there is a Moving Picture Expert Group (MPEG) coding technology. For example, a MPEG-2 standard (see Non-Patent Reference 1) and an H.264 standard (see Non-Patent Reference 2) are widely used in the fields of broadcasting technologies and accumulation technologies such as optical discs.
The standards such as digital television broadcasting currently utilized in many countries and Blu-ray Discs, have a chrominance format of 4:2:0 and an image size of 1920×1080 pixels.
On the other hand, aiming at higher image quality, future expansion of the standards has been discussed. More specifically, a chrominance format of 4:2:2 or 4:4:4, or an image size of 3840×2160 pixels would be adopted.
Such expansion of standards expansion dramatically increases a calculation amount required for decoding. Eventually, in the current technological abilities, a cost of developing a single decoder chip is high due to factors such as a processing capacity, a chip size, and a required memory bandwidth. Therefore, a plurality of chips with processing capabilities compliant with a current standard are used in parallel to deal with further expansion of the standard.
In the MPEG-2, one picture consists of one or more slices, and each slice consists of one or more macroblocks. Each macroblock consists of luminance blocks, chrominance Cb blocks, and chrominance Cr blocks. Coding is performed for each of the blocks.
An MPEG coded bitstream has such a hierarchic structure. Therefore, if a plurality of chips are used to decode a coded bitstream, there are various possible units processed by a single chip. In order to separate a coded bitstream for parallel processing, there are a conventional method of separating image data coded using MPEG into slices, and a conventional method of separating such image data based on a plurality of color components, such as luminance and chrominance (see Patent Reference 1, for example).
Among these methods, the method of separating image data into data regarding luminance and data regarding chrominance has advantages of less data transfer among chips performing parallel processing. By the above method, reference image data for motion compensation which is used by a certain single chip for decoding is only a result of decoding of the certain single chip. On the other hand, if the image is decoded after being separated spatially, into slices for example, it is necessary to control for exchanging reference image and transferring data among chips. Therefore, the technique of separating data based on luminance and chrominance is structured and controlled simpler than the method of spatially separating.
FIG. 1 is a diagram showing a conventional decoding device separating image based on luminance and chrominance in order to decode the image, which is disclosed in Patent Reference 1. In FIG. 1, the conventional decoding device, which separating image into data regarding luminance and data regarding chrominance to decode the image, includes a luminance decoder 101, a chrominance decoder 102, a luminance memory 103, a chrominance memory 104, and a synthesis unit 105.
The luminance decoder 101 and the chrominance decoder 102 receive a coded bitstream of color image data. Then, the luminance decoder 101 decodes pieces of data regarding luminance component in the color image data, and the chrominance decoder 102 decodes pieces of data regarding chrominance component in the color image data.
The luminance memory 103 stores the pieces of data regarding luminance component which have been decoded from the color image data by the luminance decoder 101. The chrominance memory 104 stores the pieces of data regarding chrominance component which have been decoded from the color image data by the chrominance decoder 102.
The synthesis unit 105 synthesizes (a) the decoded image regarding luminance component provided from the luminance decoder 101 to (b) the decoded image regarding chrominance component provided from the chrominance decoder 102.